The ATSC digital television standard presently provides for the transmission of successive data transmission fields each comprising 313 segments extending over a 24.2 ms time interval. FIG. 1 discloses an exemplary format for a data transmission field according to this standard. The first segment of each transmission field is a field sync segment. The field sync segment is composed of four two-level segment sync symbols and space for 828 other two-level symbols. A portion of this space is used for a field sync, and another portion of this space is reserved. Each of the remaining segments of each transmission field comprises four two-level segment sync symbols and 828 n-level data symbols where n is currently eight, although n could be other integers such as two, four, sixteen, etc.
As indicated by U.S. patent application Ser. No. 09/804,262 filed on Mar. 13, 2001, there is presently some interest in extending the ATSC digital television standard to allow a transmission field to contain a mix of more robustly coded data (referred to herein as E-VSB data) and the data currently provided for in the standard (referred to herein as VSB data). Preferably, although not necessarily, the data mix is employed on a segment-by-segment basis such that some segments of a transmission field are used to transmit VSB data exclusively and the remaining segments of the transmission field are used to transmit E-VSB segments exclusively. However, it is possible that all data segments of a transmission field could contain either E-VSB data segments exclusively or VSB data segments exclusively. Moreover, it is also possible that the E-VSB data contained in some segments of a transmission field may be coded at one robust coding rate and that the E-VSB data in other segments of the transmission field may be coded at other robust coding rates.
As disclosed in the above mentioned '262 application, a map that indicates which segments contain the more robust (E-VSB) data and which segments contain standard VSB data is preferably provided by the transmitter to the receiver so that the receiver can properly decode and otherwise process the received VSB and E-VSB data. Assuming that a transmission field contains E-VSB data at different coding rates, the map in that case must also designate the coding rates that apply to the differently coded E-VSB data segments.
The '262 application describes one mapping system. U.S. patent application Ser. Nos. 10/011,333 and 10/011,900 filed on Dec. 3, 2001, describe another mapping system that reliably identifies which segments contain VSB data and which segments contain E-VSB data.
Moreover, SMPTE 310M is a standard that specifies a synchronous serial interface for MPEG-2 digital transport streams between studio equipment (such as multiplexer's, encoders, decoders, ATM gateways, fiber optic interfaces, etc.) and an RF transmitter. The SMPTE 310M standard defines parameters for digitally transmitting the MPEG-2 digital transport stream with a transfer rate of 19.4 or 38.8 Mbits/sec and is primarily used for digital television applications.
E-VSB data and VSB data could be transferred between studio equipment and an RF transmitter using separate lines or channels. However, when E-VSB data and VSB data are to be combined in a field along with the map data that denotes the locations of the E-VSB data and VSB data within the transmission field, it is more desirable to multiplex the data between the studio equipment and the RF transmitter over a single line or channel.
Accordingly, one embodiment of the present invention is directed to a combination of E-VSB data, VSB data, and map data so as to provide a synchronous data link signal. This synchronous data link signal can then be transmitted over a single line or channel. In one exemplary implementation of this embodiment of the present invention, this synchronous data link signal can be arranged to meet the SMPTE 310M standard.